Passage 9.15.5
ὡς δὲ ἀφίκετο πρὸς Μαντίνειαν τῇ στρατιᾷ, νικῶν καὶ τότε ὑπὸ ἀνδρὸς ἀπέθανεν Ἀθηναίου· καὶ Ἀθήνῃσιν ἐν ἱππέων μάχῃ τὸν Ἐπαμινώνδαν ὁ ἀνὴρ οὗτος γέγραπται φονεύων Γρύλος ὁ Ξενοφῶντος, Ξενοφῶντος δὴ τοῦ Κύρῳ ὁδοῦ μετασχόντος ἐπὶ βασιλέα Ἀρταξέρξην καὶ ὀπίσω τοῖς Ἕλλησιν ἐπὶ θάλασσαν ἡγησαμένου.
When he arrived with his army near Mantineia, though victorious there also, he was slain by the hand of an Athenian. It is recorded that this man, Gryllos, the son of Xenophon, killed Epaminondas during a cavalry engagement. Gryllos was indeed the son of Xenophon, who took part in Cyrus' expedition against King Artaxerxes and afterward led the Greeks safely back to the sea.